Andrew Lansley, the leader of the House of Commons, urged backbench MPs to help the Government to keep changes to constituency boundaries.

The Commons will vote on Tuesday to try to overturn a vote by peers which effectively pushed any change to after the expected 2015 election.

Mr Lansley is understood to have told a meeting of the 1922 committee that the peers’ intervention was “constitutionally” unjustified because they are unelected.

Speaking after the meeting Conservative MPs said they expected the vote next week to be “fully whipped”. If all Tory MPs vote with the Government, along with MPs from minority parties, the result could be very close.

Last week peers voted to block the changes, which would reshape constituencies and cut the number of MPs from 650 to 600, by 2015.